Ammonium octamolybdate, (NH4)4Mo8O26 or “AOM,” is a commercially-useful molybdenum composition and is available in a variety of phases or isomers. The chemical compound referred to as ammonium octamolybdate is also commonly known variously as “diammonium catena-tetramolybdate,” “ammonium tetramolybdate,” “tetrammonium hexamolybdate,” or by CAS number 12411-64-2. Of particular interest herein is the α-phase or “α-AOM,” although other phases are known and may be used in certain applications.
α-AOM is typically produced by the thermal decomposition of ammonium dimolybdate, (NH4)2Mo2O2 or “ADM.” The thermal decomposition process occurs in accordance with the following basic chemical reaction:4(NH4)2Mo2O2+heat---->α-(NH4)4Mo8O26+4NH3+2H2O  (1)Alternatively, α-AOM also may be produced by an aqueous, or wet process, such as that disclosed in U.S. Pat. No. 4,762,700, entitled “Ammonium Octamolybdate-Alpha,” which is incorporated herein by reference for all that it discloses.
While α-AOM is commonly used as a smoke suppressant in various types of plastic materials, it may also be used in the formation of various types of optically-markable ink compositions. Such ink compositions change color in response to irradiation from light, typically from a laser, although other light sources may be used. The color change is the result of a change in oxidation state and/or the formation of non-stoichiometric products of the AOM constituent of the ink composition.
Several varieties of AOM-based optically-markable compositions or inks are disclosed in U.S. Pat. Nos. 7,485,403 and 8,048,605, both of which are entitled “Laser-Markable Compositions” and both of which are incorporated herein by reference for all that they disclose. Briefly, example ink compositions disclosed in the '403 and '605 patents comprise an oxyanion of a multivalent metal, a solvent, and a binder. The oxyanion of a multivalent metal may comprise AOM, and in particular α-AOM, although other materials are also identified. The solvent may comprise any of a wide range of solvents typically used for inks and lacquers, such as water, ethanol, ethyl acetate, isopropyl alcohol, and hydrocarbons. The binder is typically polymeric and may comprise acrylics, celluloses, polyvinyl alcohol, polyesters, and the like. The binder may further include a labile group, such as hydroxyl, acetoxy, ether acetal, or halogen. The disclosed ink compositions may also include a number of additional additives and compositions depending on a wide range of factors and desired ink characteristics, as also described in the patents.
Generally speaking, the various inks or optically-markable compositions are formed by mixing together the appropriate quantities of the AOM, solvent, and binder materials to form a lacquer. The lacquer may then be applied to the material to be marked (e.g., paper or cardboard) and allowed to dry. The actual marking or image formation process may be accomplished by directing a light (e.g., a laser beam) of suitable wavelength onto the applied ink, whereupon the color of the ink changes, thereby forming the desired image.
In addition to inks, the referenced patents also teach that AOM also may be incorporated directly into various types of polymers, such as nylon, polyesters, polyamide, polycarbonate, polyacrylate, polymethacrylate, ABS polymers, polyolefins and the like, which may thereafter be directly marked as desired in a process similar to that used for inks.